Current sensing in a switching power converter

• US 20100079125A1
• Filed: 09/30/2008
• Published: 04/01/2010
• Est. Priority Date: 07/25/2008
• Status: Active Grant

• Current Assignee: Cirrus Logic Incorporated
• Original Assignee: Cirrus Logic Incorporated
• Inventors: Melanson, John L., Gaetano, Mauro
• Granted Patent: US 8,344,707 B2
• Time in Patent Office: Days
• US Class Current: 323/285
• CPC Class Codes: G05F 1/70 Regulating power factor; Regulating reactive current or power
• CPC Class Codes: H02M 1/0009 Devices or circuits for detecting current in a converter
• CPC Class Codes: H02M 1/4225 using a non-isolated boost converter
• CPC Class Codes: H02M 3/156 with automatic control of output voltage or current, e.g. switching regulators
• CPC Class Codes: Y02B 70/10 Technologies improving the efficiency by using switched-mode power supplies [SMPS], i.e. efficient power electronics conversion e.g. power factor correction or reduction of losses in power supplies or efficient standby modes

Abstract

A power control system includes a current sense resistor located on an output side of a switching power converter. By locating the current sense resistor on the output side of the switching power converter, the current sense resistor conducts a sense current when a control switch of the switching power converter is nonconductive. Since a duty cycle of the control switch is larger for a low input voltage than for a higher input voltage, the current sense resistor conducts current for a shorter time duration for low input voltages than for higher input voltages. Thus, the root mean square (RMS) of a sense current in the current sense resistor and, thus, power dissipation by the current sense resistor, is lower during low input voltages than power dissipation in conventionally located current sense resistors. The RMS of the sense current is approximately constant across a full range of input voltages.

Claims

1. An apparatus comprising:

a switching power converter to boost an input voltage to the switching power converter to a higher output voltage during operation of the switching power converter, the switching power converter comprising;

a switch to control current to an output node of the switching power converter; and

a current sense resistor coupled to the output node of the switching power converter, wherein during operation of the switching power conductor current flows through the current sense resistor only when the switch is nonconductive.

2. The apparatus of claim 1 wherein during operation of the switching power converter (1) the switching power converter is coupled to a voltage source that provides an input voltage and (2) an average value of the current in the current sense resistor is linearly related to output power of the switching power converter for a range of root mean square input voltage values.

3. The apparatus of claim 1 wherein during operation of the switching power converter (1) the switching power converter is coupled to a voltage source that provides an input voltage and (2) for a constant output power of the switching power converter current in the current sense resistor is approximately constant.

4. The apparatus of claim 1 further comprising a controller to operate the switching power converter in continuous conduction mode.

5. The apparatus of claim 1 wherein the switching power converter is selected from a group consisting of a boost converter and a fly-back converter.

6. The apparatus of claim 1 further comprising:

an inductor coupled to an input node of the switching power converter and coupled to a node of the switch; and

a diode coupled between the node of the switch and the output node of the switching power converter, wherein the current sense resistor is coupled between the node of the switch and the output node of the switching power converter.

7. The apparatus of claim 1 wherein the switch includes a first node coupled to the output node of the switching power converter and the output node of the switching power converter is a first output node, wherein the apparatus further comprises:

an inductor coupled to the first node of the switch, wherein the switch includes a second node coupled to a second output node of the switching power converter and the current sense resistor is coupled between the second node of the switch and the second output node of the switching power converter.

8. The apparatus of claim 1 further comprising a load coupled to the switching power converter.

9. The apparatus of claim 8 wherein the load comprises one or more light emitting diodes.

10. An apparatus comprising:

a switching power converter, the switching power converter comprising;

a first input node of the switching power converter;

a second input node of the switching power converter;

a first output node of the switching power converter;

a second output node of the switching power converter;

an inductor coupled between the first input node and the second output node of the switching power converter;

a switch having a first node coupled to the inductor and a second node coupled to the second output node of the switching power converter;

a diode having a first node coupled to the second node of the switch and a second node coupled to first output node of the switching power converter; and

a current sense resistor coupled between the second output node of the switching power converter and the second node of the switch.

11. The apparatus of claim 10 wherein the switching power converter is selected from a group consisting of a boost converter and a fly-back converter.

12. The apparatus of claim 10 further comprising a controller to operate the switching power converter in continuous conduction mode.

13. The apparatus of claim 10 wherein during operation of the switching power converter (1) the switching power converter is coupled to a voltage source that provides an input voltage and (2) an average value of the current in the current sense resistor is linearly related to output power of the switching power converter for a range of root mean square input voltage values.

14. The apparatus of claim 13 wherein during operation of the switching power converter (1) the switching power converter is coupled to a voltage source that provides an input voltage and (2) for a constant output power of the switching power converter current in the current sense is approximately constant.

15. A method comprising:

boosting an input voltage to a switching power converter to a higher output voltage of the switching power converter;

operating a switch to control current to an output terminal of a switching power converter; and

generating a signal representing the current using a current sense resistor, wherein during operation of the switching power conductor current flows through the current sense resistor only when the switch is nonconductive.

16. The method of claim 15 further comprising:

receiving an input voltage to the switching power converter, wherein an average value of the current in the current sense resistor is linearly related to output power of the switching power converter for a range of root mean square values of the input voltage.

17. The method of claim 15 further comprising:

receiving an input voltage to the switching power converter, wherein for a constant output power of the switching power converter current in the current sense resistor is approximately constant.

18. The method of claim 15 further comprising operating the switching power converter in continuous conduction mode.

19. The method of claim 15 wherein the switching power converter is selected from a group consisting of a boost converter and a fly-back converter.

20. An apparatus comprising:

means to boost an input voltage to a switching power converter to a higher output voltage of the switching power converter;

means to operate a switch to control current to an output terminal of a switching power converter; and

means to sense the current using a current sense resistor, wherein during operation of the switching power conductor current flows through the current sense resistor only when the switch is nonconductive.

21. An integrated circuit to control a switching power converter, the integrated circuit comprising:

a power factor correction controller having at least one input to receive a sense signal representative of a current of the switching power converter, wherein the switching power converter includes a switch and;

(i) the sense signal represents current in the switching power converter only when the switch is nonconductive; and

(ii) the power factor correction controller is configured to generate a control signal to control conductivity of the switch and controlling conductivity of the switch controls power factor correction of the switching power converter.

22. The integrated circuit of claim 21 wherein during operation of the switching power converter (1) the switching power converter is coupled to a voltage source that provides an input voltage and (2) an average value of the current in the current sense resistor is linearly related to output power of the switching power converter for a range of root mean square input voltage values.

23. The integrated circuit of claim 21 wherein during operation of the switching power converter (1) the switching power converter is coupled to a voltage source that provides an input voltage and (2) for a constant output power of the switching power converter current in the current sense resistor is approximately constant.

24. The integrated circuit of claim 21 wherein the power factor correction controller is configured to operate the switching power converter in continuous conduction mode.

25. The integrated circuit of claim 21 wherein the power factor correction controller is further configured to:

generate a high value of the control signal, wherein the switch conducts during the high value of the control signal; and

determine an amount of time T2 for a low value of the control signal, wherein the switch is nonconductive during the low value of the control signal, wherein determining the amount of time T2 is determined from;

T2B(n)=[(T2A(n)+T2B(n−

1)]/2,

wherein T2A(n) represents a first portion of the amount of time T2 and T2B(n−

1) represents a remaining portion of the amount of time T2 from an immediately preceding cycle of the control signal.

26. A method of control a switching power converter, the integrated circuit comprising:

receiving a sense signal representative of a current of the switching power converter, wherein the switching power converter includes a switch and the sense signal represents current in the switching power converter only when the switch is nonconductive; and

generating a control signal to control conductivity of the switch, wherein controlling conductivity of the switch controls power factor correction of the switching power converter.

27. The method of claim 26 wherein during operation of the switching power converter (1) the switching power converter is coupled to a voltage source that provides an input voltage and (2) an average value of the current in the current sense resistor is linearly related to output power of the switching power converter for a range of root mean square input voltage values.

28. The method of claim 26 wherein during operation of the switching power converter (1) the switching power converter is coupled to a voltage source that provides an input voltage and (2) for a constant output power of the switching power converter current in the current sense resistor is approximately constant.

29. The method of claim 26 further comprising:

operating the switching power converter in continuous conduction mode.

30. The method of claim 26 further comprising:

generating a high value of the control signal, wherein the switch conducts during the high value of the control signal; and

determining an amount of time T2 for a low value of the control signal, wherein the switch is nonconductive during the low value of the control signal, wherein determining the amount of time T2 is determined from;

T2B(n)=[(T2A(n)+T2B(n−

1)]/2,

wherein T2A(n) represents a first portion of the amount of time T2 and T2B(n−

1) represents a remaining portion of the amount of time T2 from an immediately preceding cycle of the control signal.